1. Field of the Invention
The techniques disclosed herein relate to the technical field of coating joint portions of body panels of an automobile with a sealer material.
2. Description of the Prior Art
As is generally known, for example, in a body coating step used in an automobile manufacturing factory, a filler consisting of a highly viscous material, such as a sealer, is applied as a sealing material along a seam between predetermined panels, which have been joined by spot welding, so as to form an automobile body. In this coating step, measures for preventing leakage of rainwater around the body and techniques for preventing rusting and corrosion thereof are employed.
A conventional highly viscous material coating apparatus may be adapted to automatically coat the joint portions of such panels with a sealer material. For example, a playback-type coating robot may be used. However, when such conventional apparatus is used, it is difficult to coat the joint portions of the panels with a sealer material as accurately and as quickly as in a similar manual coating operation while maintaining the relative positions of the automobile body and the coating apparatus during the coating operation. This difficulty is ascribed to the following. It is unavoidable in practice that the joint between the panels in each unit of an automobile body deviates to a considerable extent due to accumulated error caused by deviation of a body transfer conveyor, failure in alignment of the body with a carriage on which the body is loaded, failure in alignment of the body with a jig when the body is loaded on the carriage, and assembly error within the body itself.
Above all, the door, hood and trunk lid in an automobile body cannot accurately be coated with a sealing material, not only because of such accumulated error but also because of fitting error. Namely, unlike a conventional manual coating operation, conventional automatic coating apparatus is substantially incapable of compensating for such errors and of applying a sealing material accurately and narrowly along a joint between the body panels. This makes it impossible to obtain a satisfactorily high coating accuracy.
Under the circumstances, the following systems have recently been devised and used for coating an automobile body with a highly viscous material.
One such system is a system for setting a coating apparatus on a body shell or a door panel fitted therein, detecting the deviation of the position of the coating apparatus as set, adding the detected quantity of positional deviation as a correction quantity to a program that operates the coating apparatus, and carrying out a coating operation with the positional deviation eliminated. Another such system detects positional deviation of a joint of body panels from a target point on the coating apparatus and inputs a signal representative of the detected deviation into the coating apparatus for use as a coating-apparatus controlling feedback signal, thereby to control the apparatus so that the target point is aligned with the joint.
However, when the coating apparatus in these types of conventional systems are used for coating a curved surface of a workpiece, especially a structure having a complicated three-dimensional curved surface such as an automobile body, the position detector and controller are complicated in construction and are very expensive. Moreover, in such former systems, the position detector requires a certain period of time to carry out the position detecting operation and to correct the operating program. This causes inconvenience in the coating operation, i.e. loss of operation time of a robot. In the latter system, it is necessary to provide a detector on, or in the vicinity of, the coating apparatus. Therefore, the detector interferes with a member of the body being coated so as to greatly restrict the range of the coating operation.
In order to eliminate these inconveniences which adversely affect the practical operation of the coating apparatus, a system has also been employed that is provided with a plurality of types of coating apparatus which are suitably used for coating different types of parts of a workpiece, to enable the coating apparatus to be applied to the largest possible number of portions of an automobile body. However, arranging the coating apparatus in this manner not only causes an increase in the number of different coating apparatus that are required but also an increase in the number of coating steps. Also, such a practice increases both the dimensions of the space required and the manufacturing cost. Since different coating apparatus are used for different types of workpiece portions to be coated, the adaptability of these systems to different types of automobiles is lowered. Furthermore, the robots, as coating apparatus, make many useless actions, and the number of required coating steps increases.
At present, there are a very limited number of robots which are capable of coating a workpiece having a complicated three-dimensional curved surface, such as a door assembly, with high accuracy and at a speed as great as that at which a conventional manual coating operation is carried out. The equipment is greatly limited. Moreover, for a sealing action of the robot, the coating apparatus is required to have an accuracy of around .+-.1-2 mm with respect to an instruction at each point. Consequently, a number of troublesome steps are required for providing such instructions.
Under the circumstances, there has been a demand for the development of a slim, compact, inexpensive, versatile, and easily-operable coating apparatus having the advantage of using a commercially-available non-modified industrial robot of small volume and capable of carrying out coating and profile coating operations with respect to each portion of a workpiece with the required sufficiently-high accuracy, without limiting the coating steps, and without interfering with a workpiece, even a workpiece having a complicated three-dimensional construction such as an automobile body.